Ultra high strength alloy steels



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United States Patent O 3,164,495 ULTRA HIGH STRENGTH ALLOY STEELS ClydeA. Furgason, Milwaukee, Wis., assignor to Ladish Co., Cudahy, Wis., acorporation of Wisconsin N Drawing. Filed Sept. 26, 1961, Ser. No.140,67

1 Claim. (Cl. 148-36) A This application is a continuation-impart of myapplication Serial No. 82,969, filed January 16, 1961, now

abandoned. e t

This invention relates to improvements in ultra high strength alloysteels and particularly to a steel that con tains a minimum of strategicalloying elements while possessing high yield and ultimate strength whentempered at high temperatures and the 'ability to maintain high strengthat elevated temperatures.

Users and manufacturers of hot work tool and die steels are constantlylooking for improved steels which are stronger, tougher, have higherimpact resistance, and can withstand higher temperatures. Most hot workdie steels possess a secondary hardening characteristic which provideshigher temperature resistance because high hot hardnesses can beobtained and'retained whentempering at high temperatures. At the sametime, these steels must be capable of being hardened deeply. j

. Prior to the present invention, the lowest alloy analysis which wouldimpart secondary hardening was generally considered to be an alloycontaining no less than 7% total alloying elements.

It is therefore an object of this invention to provide an alloy steelanalysis containing only approximately 4% total alloying elements, thatis deep hardening and possesses a secondary hardening characteristicplus good ductility. The alloy steel of this invention is applicable tocritical hot work tool and die applications as wellas to ultra highstrength structural applications subject to elevated temperatures andboth dynamic and static loading.

Aircraft, and more recently missile, manufacturers have been constantlyseeking newer and better materials for utilization on critical partswhere high strengths and strength/ weight ratios could bring aboutsubstantial weight savings on the vehicles. Coupled with this trendtoward lighter weight, higher strength is the increase in speed with anaccompanying aerodynamic heating problem. This has necessitated highstrength materials which are capable of withstanding sustained elevatedtemperatures without losing strength and ductility. v

The abilities of aircraft and missilestructural materials to performunder these conditions has necessitated a shift from the A131 4340 typematerial and its modifications to the more highly alloyed materials (forexample SAE H- 11) (0.40% C, 5.0% Cr, 130% Mo,0.50% V).

The reason for this shift is the need for a steel which 1 essary, makingit particularly suitable for elevated "temcan be heat treated to tensilestrengths of 220,000 to 280,000 psi and retain suflicient toughness forlanding gear, engine mounts, hot work tools and dies, and otherstructural applications. A greater problem was to provide an alloy steelcapable of being. heat treated to these high strengths and .at the sametime maintain its strength:

3,164,495 Patented Jan. 5, 1965 works which adversely affect the heartreat response if cooling from the hot working temperature is notprecisely controlled or executed properly. It has heretofore beengenerally believed that H-ll is the lowest alloy analysis that willimpart secondary hardening.

It is therefore an object of the present invention to provide animproved alloy steel that possesses an extremely low alloying elementcontent, thereby using a minimum of strategic materials, whilepossessing secondary hardening characteristics with good ductilityespecially at room temperature.

It is a further object of the invention to provide an alloy compositionthat posesses secondary hardening characteristics while only containingapproximately 4% total alloy content, said alloy also possessingexcellent high strength and toughness properties.

Many of the so-called ultra high strength steels rely on high Siliconcontents to reduce temper brittleness while producing high strengthlevels when tempering between 400 F. and 700 F. It is therefore anobject of the invention to provide an alloy steel which exhibits highstrength with adequate ductility when tempered in excess of 1000 F.,thereby providing maximum stress relief of quenching stresses as well aspermitting distortion correction at high temperatures where correctionis much simplier.

It is a further object of the invention to provide an alloy steel whichrestricts the amount of the alloying element silicon to less than 0.5thereby maintaining high stress rupture properties. Silicon contents inexcess of 0.5% results in degradation of said stress rupture properties.

A still further object of the invention is to provide alloy steel whichmaintains higher elevated temperature stability than other secondaryhardening alloys.

In the alloys of my prior patents Nos. 2,919,188, dated December 29,1959, and 2,921,849, dated January 19, 1960, if it were attempted toheat treat to ultra high strength levels, the tempering temperaturewould have to be substantially lower than with the present invention asthere would be considerably less relief of quenching stresses.duringtempering at the low temperature. The results of the presentinvention are obtained principally by substantially increasing theamount of molybdenum over that contained in the alloys of my. priorpatents, whereas to obtain the results of the present invention it wouldbe conventional practice to substantially increase the amount of chrometo a level substantially affecting the cost of the alloy, as. comparedto the cost when molybdenum is moderately increased as in the presentinvention.- i

A further object of the invention is to provide an alloy steel which issuitable for use where superior toughness, wear resistance, elevatedtemperature strength, stress rupture strength and high impact loadresistance are necperature structural, die and tool steel applications.

A further objectof the invention is'to provide'an alloy steel whichexhibits superior properties'at room temperature when heat treated to apredetermined high tensile strength range, the .alloy retaining highstrength at elevated temperatures so that it can be used forapplications where high strength at both room temperatures and elevatedtemperatures is required.

A further object is to provide an alloy steel which maintains a highyield to ultimate ratio at all strength levels up to 280,000 p.s.i.

A further object is to provide an alloy steel of low creep rate' atelevated temperatures so that the material may be used whereapplications at high temperature stress are required for prolongedperiods of time.

Other objects are to provide an alloy steel which exhibits lessdistortion in quenching, and which is weldable in heavy sections, while.employing techniques and controls normally used in welding medium carbonlow 4 v materials need be employed to obtain prop'ertiesiheretm foreobtained by a much higher alloy content.

The following tables indicate the improved properties of the alloy steelof the present invention.

An average of the room temperature' mechanical prop-: erties of thepresent alloy steel afterf normalizing at 1900 F., air quenching from1850 F., as shown, are summarized in Table I.

strength of 265,000v to 275,000 p.s.i. a yield strength of 235,000 to255,000 p.s;i. elongation of 910%, and a reduction of area of -45%.

TABLE I Mechanical Properties at Room Temperature, Air

Quenched From 1850 F. and Tempered as Shown Percent Percent RockwellOharpy Temper U.S., Y.S., Elong. Red. 0 V-Notch Temp., F. p.s.i p.s.i.m2" of Area Hardness Inpacts,

' ft. lbs

formula without causing brittleness while the product maintainsductility and good weldability. It has also been discovered that amoderate increase in the amount of molybdenum over that of my priorpatents, heretofore referred to, will permit 'heat treatment to ultrahigh strength levels While tempering at a high temperature to provideless likelihood of distortion from stresses.

The alloy of this invention 'has the following contents in percent:

Mn e. 57-.93.

P .010-maximum. S -2 .010 maximum. V Q. .49.61.

Remainder iron with residual impurities.

It is important to maintain a relatively low phosphoru and sulfurcontent. 7

A desirable formula for many purposes is:

C e .48 approximately. Mn --i .75 approximately. Si -35 approximately.Ni .55 approximately. Cr 1.00 approximately. Mo 2.00 approximately. P.010 maximum.

S .OIOmaximum.

V .50 approximately.

Remainder iron with incidental impurities. v

The above formula may be modified by the addition of other elementsandthe present invention is not to be construed so as to preclude theuse of small amounts of such elements as uranium-23 8, tungsten,columbium, or rare earth elements in the basic composition.

It is apparent from the above total that the alloy con tent is very lowso that only a minimum of strategic The short time elevated temperatureproperties of the alloy steel of the present invention when austenizedat 1850 F. and tempered at 1050 F. to produce the maximum strength inthe secondary hardening tempering range are summarized in Table II. Thetest temperatures are below the corresponding'temper temperature tosimulate treatment necessary to be compatible with operatingtemperatures, i.e., the tempering-temperature must be higher than theoperating-temperature to prevent tempering the material while inoperation.

'The elevated temperature data shows the yield and ultimate strengths tobe well above 170,000 p.s.i. at 900 F. test temperature, and at 1000 F.test temperature the ultimate strength is 185,000 p.s.i. andthe yieldstrength is 162,720 p.s.i. With these high elevated temperaturepropertiesflhe present alloy is desirable for elevated temperaturestructural application. This data is "indicative of propertiesobtainable when designing to operating temperature ranges. i

TABLE II Short Time Elevated Temperature Mechanical Properties [Heattreatmenti Normalized, 1,900 F.; air quenched, 1,850 F.; temperedasshown] Temper. Test Temp., Ult. Stu, Yield Elong. Red. of. 'Iemp., F.p.s.i. p.s.i. Percent Area,

7 Str. p.s.i. Percent Charpy V-Notch impact properties, heat treated to260,000 p.s.i. to 280,000 p.s.i. strength level and tested at elevatedtemperatures are shown in Table III.

Th' maximum ultimate and yield strength with adequate ductility, asmeasured by the percent elongation and reduction of area, is achieved bytempering between 1000 F. 1100 F. This temper produces an ultimatetensile? "TABLE I11 Elevated Temperature Impact Properties [Normalized,1,000 E; air quenched, 1,850 F4 tempered, 1,050 El ELEVATED TEMPERATURESTAR'ILITY The elevated temperature stability of the present alloy issummarized in Table VII. The ultimate and yield strength remainunchanged, for all practical purposes,

5 with uniform ductility, as measured by the percent elon- 1 3 a 1 1 t'r ft 100 h 1 Test Temp.,F. Ft. Lbs. ga n an re ucion 0 area, evena erours 0 Ft. Lbs. Ft. Lbs. Ft. Lbs. stabilizing at 1000 F,

19 ,18 18 p 18.3 TABLE VII -22 1 23 22 22.5 ;22 23 23 0 22.7

23 20 21.2 Elevated Temperature Stability T elzszle Properties 20 23 2725.6 1 1 g2 [Heat treatment: Normalized, 1-,900 F.; Air quenched, 1,850F.;te1nv 27 I 26 0 pered at 1,050 F. Specimens held at 1,100 F. for timeindicated and L testedat room temperature] 1 25 25 25.5

Ultimate Yield Elong. Red. of TABLE IV Timeat1,000 F.Hrs Str.,p.s.i.Str.,p.s.i. percent Area, per- 08D Modulus of Elasticity 20388 a: 12-Mdul IE1 t- .5 TestTemp F) f 5 1 203, 200 247,900 9.0 30.3

80 3m RooM TEMPERATURE MECHANICAL PROPERTIES AT Am 214 STRENGTH LEVELSOF 180,000-200,000 p.s.i., AND 200,000- m 2 0 220,000 p.s.i. 000 26.7700 27.1 25 The data m Table VIII shows additional room temperafi 321gture mechanical properties for the above two strength 1,000 24.9 levels.The data further exhibits the higher strength levels obtainable with thesteel of the present invention.

TABLE VIII Room Temperature Mechanical Properties at 200,000 220,000p.s.i. Strength Level V-Notch Charpy Norm. Quench Temper Ult.Str., YieldElong, Bed. of Impact Temp, Temp.,1*. Temp, p.s.i. Str.p.s.i. percentArea, (Avg.6 F. F. percent Tests),

Ft.Lbs.

Angle of bend, 180 for each of the above heat treatments.

TABLE v sTREss RUPTURE PROPERTIES 10min}, End Quench Hardenability Thestress rupture propertles of the improved alloy h dE d Ext th are shownin Table 1X. The propertles are excellent up [Dmme mm the Queue e n em8)] to 1000" F. test temperature and stresses up to 100,000

.s.i. Quench 'I;emp. 1 2 3 4 5 0 8 10 12 14 16 20 24 28 32 p TABLE 1X 5857 57 57 57 50 50 55 54 53 52 50 56 55 50 55 50 50 55 55 55 54 54 StressRupture Properties 55 55 55 54 54 54 54 54 53 53 53 53 55 [Normalized,1700 F.; tempered, 1050 F.]

cREEP RUPTURE PROPERTIES The creep rupture properties of the improvedalloy Test -N ggl r s t g heat treated to 260,000 to 280,000 p.s.i.strength level are shown in Table VI. The properties show a very low1006007 98 9 creep rate at temperatures of 950 F. and 1000" F. This901000 14813 material may be used where applications of high tem- $8 38322 2-: perature and stress are required for prolonged periods of time.

TABLE VI Creep Rupture Properties [Normalized, 1,850" F.; doubletempered, 1,050 11. All tests terminated after 500 hours] It will beunderstood that it is desired to comprehend within the invention and thescope of the claim thereof such equivalent materials and proportions asmay be found necesary to adapt this invention to the varying conditionsmet in actual practice and we do not limit ourselves to these specificmaterials and proportions.

60,000 What I claim is:

7 -0074 An improved alloy steel consisting essentially of about .40.55%carbon, about .57 to .93% manganese, about Stress, p.s.i. Creep, per-Test Tem F.

p centin50hrs.

7 .23-.45% hsilicon, about 351.70% tnickel about .87- cl.23 Chromium, upto 1,0 10% pho sphor-ugup'vto about .Q l,0%. ulflur, about 1 .88 2.27molybdenum in. combinationwith about -.49. ,.61%;vanadiurn to produce asec- :ondary -hardening characteristic,v and the remainder beingironyvith incidental impurities, and the metal having the ability tomaintain high strength considering itsi low alloy content for prolongedperiods of elevated temperatures with accompanying good ductility, therebeing an absence of temper brittleness when tempered at 10W;10temperingtempqratures, said talloy .steellhavinglbeennheat treated byaustenitizing at 1800 F.1900 F. followed by quenching, and subsequenttempering between 1000 F.

to 1100 F. I

References,(l'itedpbytthe Examiner UNI-TEDSTATES-PATENTS 2,327,490 "8/43iBagSar 75 128.85 5 "2,919,188 "'12/59 -Furgason f75"128;85 2,921,849 1/60 Furgason 75128.85

-OTHER-REFERENCES Archer ,et al.: Molybdenum-Steels, Irons, Alloys,jClimax Molybdenum Company; New York, September 12, 1949,-page 10,FIG.'"7 relied' upon. 1 {DAVID L.: RECK, 'Primm y iExaminer.

RAY K. WINDHAM, Examiner.

